Historically car audio equipment is self-contained without any cable interfaces to handheld devices. With the introduction of mobile phones there came a first need to smoothly interface these mobile phones to the car equipment. Operating these devices during driving the car has created a potential safety risk when the driver looses the attention to the traffic. For that reason all kind of CAR-Kits where introduced in order to keep better control via the controls of the car. With that CAR-Kits the mobile phone is installed e.g. in a docking station or the mobile phone is connected via wireless communication like Bluetooth to the CAR-Kit.
Now that modern handheld solid-state digital audio devices, like an iPod and MP3-players in general, are becoming more and more popular another connectivity problem arises. These devices usually do not have a wireless connectivity like Bluetooth that is being used for mobile phones to link up to the car equipment.
Besides this there are two other reasons why this is not appropriate. First of all the available bandwidth is insufficient to transport HiFi stereo audio signals. Secondly these devices provide copyright protection mechanisms to prevent copying copyrighted digital audio material.
This only leaves the option open to connect the device with an analogue audio link. A second digital link must be provided to enable the car controls to control the device. This however does not prevent to not connect the control link so that the user could still use the controls from the device and thus a safety risk is introduced again.
US 2006/0245364 A1 discloses a bi-directional continuous voice and video quality testing system for measuring a communication link.
EP 1698518 A2 discloses a multimedia device integration system for vehicles wherein the multimedia device integration system can control an external device like a CD-player or a digital media player and a control information is passed between the car stereo system and the external device.
US 2003/0188005 A1 discloses a data stream-distribution system between an audio player and a server.